Modern high strength-to-weight ratio fibers make it possible to construct high energy density flywheels, which, when combined with a high power motor-generators, are an attractive alternative to electrochemical batteries for use as energy buffers in hybrid electric vehicles. A properly designed flywheel system would provide higher energy density, higher power density, higher efficiency, and longer life than a conventional electrochemical battery.
The vehicle environment, however, presents special challenges to successful implementation of a flywheel to motor vehicle applications. Among these challenges are the need to deal with the gyroscopic torques resulting from the vehicle's angular motions and the need to compensate for translational accelerations of the vehicle. Several safety issues resulting from the high energy and momentum stored in the flywheel also need to be taken into account, as does the difficulty of cooling the motor-generator operating in a vacuum chamber. In addition, energy conservation considerations and user convenience dictate the requirement that the flywheel storage system possess a slow self-discharge rate.
Flywheel energy storage systems have been proposed for many years; many of the storage systems have even been proposed for use in motor vehicles. U.S. Pat. No. 3,741,034, for example, discloses a flywheel contained in an evacuated sphere which is surrounded by a liquid and having various safety features. However, the '034 patent does not address waste heat production and the requirement for cooling the motor-generator. In addition, the '034 patent does not address itself to the dynamics of the driving environment, or the minimization of the power drain when parked.
U.S. Pat. Nos. 4,266,442, 4,285,251 and 4,860,611, on the other hand, disclose different ways of constructing high speed rotors. However, the above referenced patents do not recognize, let alone describe, design features needed for compatibility with the environment of a motor vehicle.
The present invention was motivated by a desire to correct the perceived weaknesses and identified problems associated with conventional flywheel energy storage systems.